Process for the extraction and recovery of aromatic hydrocarbons



- l, 1970 H. L. THOMPSON $544,453

PROCESS FOR THE EXTRACTION AND RECOVERY `OF ARMATIC HYDROCARBONS FiledDec. 5, 1968 //V V EN TOR:

Herbert yf/e Thompson A TTORIVEYS Unted States Patent O U.S. Cl. 208-3217 Claims ABSTRACT OF THE DISCLOSURE Process for the recovery of aromatichydrocarbons utilizing the steps of solvent extraction, water Washing ofthe raflinate phase, recovery and reuse of the wash water, andfractionation of the extract phase. Sulfolane is the preferred solventand benzene is recovered as a preferred product stream.

BACKGROUND OF THE INVENTION The present invention relates to the solventextraction of aromatic hydrocarbons from a hydrocarbon charge stream.More particularly, the present invention relates to the recovery ofsolvent from the rainate stream produced in the process of extractingaromatic hydrocarbons from a hydrocarbon charge stream. Morespecifically, the present invention relates to an improved process forthe recovery of solvent from the rainate stream by means f an improvedwater wash technique.

It is well known in the art that the non-aromatic hydrocarbon raflinatewhich leaves the extraction zone of an aromatic hydrocarbon extractionprocess contains contaminating quantities of solvent. This solvent whichcontaminates the Iainate stream must be recovered not only because itmay interfere with subsequent raffinate processing or ultimate ratlinateuse, but also because continual loss `of solvent is a prohibitiveeconomic expense in a commercial aromatic extraction process utilizingmodern technology.

A typical solvent which is utilized in commercial aromatics extractionplants and which may be recovered in accordance with the practice ofthis invention is a solvent of the sulfolane-type. This solventpossesses a iive membered ring containing one atom of sulfur and fouratoms of carbon, with two oxygen atoms bonded to the sulfur atoms of thering. Genetically, the sulfolane-type solvents may be indicated ashaving the following structural formula:

RlC \CH-R4 Rz-tllH-tllH-Ra wherein R1, R2, R3, and R4 are independentlyselected from the group comprising a hydrogen atom, an alkyl grouphaving from one to ten carbon atoms, an alkoxy radical having from oneto eight carbon atoms, and an arylalkyl radical having from one totwelve carbon atoms. Other solvents which may be included Within thisprocess are the sulfolenes such as 2-sulfolene or 3sulfolene which havethe following structures:

Other typical solvents which have a high selectivity for separatingaromatics from non-aromatic hydrocarbons and which may be processedwithin the scope of the Patented Dec. 1, 1970 ICC present invention areZ-methylsulfolane, 2,4-dimethylsulfolane, methyl 2-sulfonyl ether,n-aryl-3-sulfonyl amine, 2-sulfonyl acetate, diethylene gycol, variouspolyethylene glycols, dipropylene glycol, various polypropylene glycols,dimethyl sulfoxide, N-methyl pyrollidone, etc. The specificallypreferred solvent chemical which is processed within the scope of thepresent invention is sulfolane, having the following structural formula:

Because the typical solvents which are utilized in aromatics extractionare water soluble, it is the practice of the art to extract the solventfrom the raflinate stream by Washing with water in a subsequentcontactor. The extraction of the solvent from the raffinate with watermay be undertaken in any suitable liquid-liquid contacting means, as ina tower containing suitable packing such as Berl Saddles or RaschigRings, or in a tower containing suitable trays, or in a rotating disccontactor (RDC). The solvent may then be readily recovered from theaqueous solution by distillation.

It has been descovered in the commercial aromatics extraction units thatthe recovery of sulfolane-type solvent from the raffinate by extractionwith Water does not correspond to the recovery which is to beanticipated based upon solubility data, and the assumption of reasonableeiliciency of the extractor. Thus, the loss of sulfolane in the rainateproduct has been found to be from live to eight times as great asanticipated, and this loss is greatly above what is economicallydesirable.

SUMMARY OF THE INVENTION Therefore, it is an object of the presentinvention to provide a process for the extraction and recovery ofaromatic hydrocarbons from a feed mixture containing aromatic andnon-aromatic hydrocarbons with a sulfolane-type solvent.

It is another object of this invention to provide an improved processfor the recovery of solvent from the rainate stream utilizing waterwashing in a facile and economical manner.

It is a still further object of this invention to provide a process forthe production of a rainate product stream from an aromatic extractionprocess which is substantially free of solvent contaminant.

Accordingly, the present invention provides a process for the extractionand recovery of aromatic hydrocarbons from a feed mixture containingaromatic and nonaromatic hydrocarbons with a sulfolane-type solventwhich comprises the steps of: (a) introducing said feed mixture into asolvent extraction zone maintained under aromatic hydrocarbons with asulfolane-type solvent presence of said sulfolane solvent suticient toproduce an extract phase comprising said solvent having aromatichydrocarbons dissolved therein, and a reaftinate phase comprisingnon-aromatic hydrocarbons contaminated with small quantities of saidsolvent; (b) passing said extract phase into fractionation recoverymeans under fractionation conditions including the presence of strippingsteam from a source hereinafter specified sufficient to produce adistillate vapor fraction comprising aromatic hydrocarbons and steam anda bottoms fraction comprising lean solvent suitable for reuse in saidextraction zone; (c) condensing said distillate vapor fraction andproducing thereby a product stream comprising aromatic hydrocarbons andan aqueous stream; (d) introducing said reainate phase into a first washzone in contact with said aqueous stream of Step (c) under conditionssucient to absorb at least a portion of said contaminant into theaqueous stream; (e) withdrawing from said rst wash zone a non-aromatichydrocarbon stream having reduced contaminant content, and a rst richwater stream containing solvent; (f) passing said non-aromatichydrocarbon stream into a second wash zone in contact with `ahereinafter specified wash water stream under conditions `suflicient toabsorb substantially all of the remainder of said solvent contaminantinto the wash water stream; (g) removing from said second wash zone anon-aromatic hydrocarbon stream substantially free of solventcontaminant, and a second rich water stream containing solvent; (h)introducing said second rich water stream into a fractionation zoneunder fractionation conditions suicient to produce a distillate waterstream substantially free of said solvent and a bottoms streamcomprising water containing said solvent; (i) passing said distillatewater stream of Step (h) into said second wash zone as the specied washWater; and, (j) introducing at least a portion of said rst rich waterstream and said bottoms stream of Step (f) into said recovery means ofStep (b) as the specified source of stripping steam.

In essence, therefore, it can be seen that the present inventionutilizes a two-stage water wash technique of the raflnate stream whichoperates in conjunction with a separate water distillation means for`the production of'separate and distinct wash waters for use in thetwostage water washing technique. In addition, it can be readily seenthat the present invention embodies the unique concepts of water reusein a facile and economical manner.

DETAILED.DESCRIPTION OF THE INVENTION As a broad general class, suitablefeedstocks for the satisfactory practice of this invention include fluidmixtures having a sui'liciently high concentration of aromatichydrocarbons to economically justify` recovery of these aromatichydrocarbons as a separate` product stream. The present invention isparticularly applicable to hydrocarbon feed mixtures which contain atleast 25% by weight aromatic hydrocarbons. A suitable carbon numberrange for the feedstock is from about 6 carbon atoms per molecule toabout 20 carbon atoms per molecule and, preferably, from about 6 to 10carbon atoms per molecule. One suitable source of feedstock is thedebutanized reactor eiuentfrom a conventional catalytic reformingprocess unit. Another suitable source of feedstock is the liquidby-product from a pyrolysis gasoline unit which has been hydrotreated tosaturate olelns and diolens thereby producing an aromatic hydrocarbonconcentrate suitable for the solvent extraction technique describedherein. Typically, the feedstock from a catalytic reforming processcontains single ring (monocyclic) aromatic hydrocarbons comprising awide boiling mixture of benzene, toluene, and xylenes. These single ringaromatic hydrocarbons are also mixed With the corresponding paraffinsand naphthenes which have been pro-` duced from such a catalyticreforming unit.

As previously mentioned, the preferred solvent which may be utilized inthe present invention is a solvent of the sulfolane-type. Since thissolvent is an article of commerce and is well known to those versed inthe solvent extraction art, greater detail thereof need not be presentedat this time.

The aromatic selectivity of the solvent can usually be enhanced by theaddition of water to the solvent. Pref-` tractor-stripper following theextraction zone, more fully discussed hereinafter, to vaporize the lasttraces of nonaromatic hydrocarbons from the solvent stream by steamdistillation. Accordingly, the solvent composition of the presentinvention preferably contains from about 0.1% to about 20% by weightwater and, preferably, about 0.5 to about 1.0% by weight depending uponthe particular solvent utilized and the process conditions at which theextraction zone and the extractor-stripper are operated.

The solvent extraction zone of the present invention is. operated atelevated temperature and sufficiently elevated pressure to maintain thefeedstock, the solvent, and any reflux streams in liquid phase.Typically, suitable temperatures, when using sulfolane las the solvent,are Within a range from about F. to about 400 F. and, preferably, fromabout 175 F. to about 300 F. Similarly, suitable pressures are generallywithin the range from about atmospheric pressure up to about 400p.s.i.g. and, preferably, from l50 to 150 p.s.i.g.

This invention also embodies the concept of displacement of non-aromatichydrocarbons from the extract phase at the lower end of the extractionzone by utilizing the technique of a non-aromatic hydrocarbon containingreux at that point. Itis distinctly preferred that this reflux streamcomprise relatively light non-aromatic hydrocarbons, but may containsignilicant quantities of aromatic hydrocarbons, e.g. from 30% to 60% byweight. In other words, the extractive distillation column following theextraction zone is operated in such a manner that a reux stream isobtained which comprises a concentrate of nonaromatic hydrocarboncomponents which were left in the extract phase from the extractionzone.

The amount of reflux introduced into the lower end of the extractionzone may be varied considerably depending upon the degree to whichnon-aromatic hydrocarbons are being rejected in the extraction zone. Itis preferred that the relatively light non-aromatic reflux introducedinto the lower end of the extraction zone be at least 10% by volume ofthe extract phase in order o elfecively displace non-aromatichydrocarbons from the extract phase into the rallinate phase.

The extractive distillation column following the extraction zoneutilizes the extract phase as feedstock and is operated at moderatepressures and `sufficiently high reboiler temperatures in order tovaporize all of the nonaromatic hydrocarbon material and a portion ofthe aromatic hydrocarbons, water, and solvent out of the bottom portionof this column. It is preferred that this first distillation column beoperated substantially as a stripper column although fractionation orseparation does, in fact, take place therein; that is, the extract phaseshould be fed into this column at the upper portion thereof in order toprovide maximum stripping to take place in' the column. In order forextremely high purity aromatic hydrocarbons to be ultimately obtained,it is essential that the extractive stripper column be operated in amanner to prevent all except minute traces of non-aromatic hydrocarbonsfrom being withdrawn in the bottoms product stream from the lower end ofthis column.

Typically, the extractive stripper will be maintained under pressuresfrom atmospheric to about p.s.i.g., although generally the top of thestripper column is maintained at from 7 p.s.i.g. to about 20 p.s.i.g.The reboiler temperature maintained in the extractive stripper is, ofcourse, dependent upon composition of the extract phase feed thereto andthe solvent. The column is arranged to take only an overhead fractionand the bottoms fraction as separate product streams. Those skilled inthe art, from a knowledge of the prior art and the teachings presentedherein, are well versed in the operation of an extractive strippercolumn of this type and, therefore, additional details thereof need notbe presented here.

The aromatic and solvent recovery column is operated at low pressuresand sufficiently high temperatures to distill the aromatic hydrocarbonsoverhead as a distillate fraction thereby producing a bottoms fractioncomprising lean solvent which is generally suitable for reuse in thesolvent extraction zone. Again, the precise choice of operatingconditions depends upon the feedstock characteristics including aromatichydrocarbon content and the composition of the solvent. Preferably, thetop of the aromatic recovery column is operated at about 100 to about400 mm. Hg absolute. These subatmospheric pressures must be employed inorder to maintain a sufficiently low reboiler temperature to avoidthermal decomposition of the solvent, particularly when the solvent isof the sulfolane-type. Preferably, the reboiler temperature should bemaintained below about 360 F. when using saturated sulfolane as thesolvent.

Returning now to the operation of the extractive stripper column: theoverhead stream from the extractive stripper column is in the vaporstate and comprises primarily non-aromatic hydrocarbons of the naphtheneand/ or paraffin type. Typically, this vapor stream together with avapor stream from a water stripper column, hereinafter described arecondensed in a common condenser thereby producing a combined hydrocarbonstream and a Water stream. It is this condensed hydrocarbon stream whichis preferably utilized as reflux in the extraction zone in the mannerpreviously discussed.

Returning to the solvent extraction zone description: the rafiinateleaves the aromatic extraction zone at an elevated temperature, iscooled, and passed into a first water wash column. This first water washcolumn, typically, is a vertically disposed vessel containingconventional liquid-liquid contacting apparatus, such as Berl Saddlesand other packing material. The cooled raffinate stream enters the lowerend of the column and passes upwardly in counter-current fashion incontact with a first water Wash stream, the source of which ishereinafter discussed, which is introduced into the upper portion of thecolumn. Suitable operating conditions are maintained in the first waterwash column so that, preferably, at least a significant portion ofsolvent contaminant which was in the raffinate phase is absorbed into`the water phase. Thus, a first rich water stream containing theextracted sulfolane is withdrawn from the bottom portion of the firstwater wash zone, and a hydrocarbon stream having a reduced solventcontaminant content is withdrawn from the upper portion of the firstWater wash column.

The hydrocarbon stream comprising the hydrocarbons of the raffinatephase, and having a significantly reduced solvent content, is thenpassed into a second Water wash zone, similarly constructed to the firstwater wash zone, such that the hydrocarbon stream is countercurrentlycontacted with a second water wash stream, from a source hereinafterdescribed, under conditions sufficient to produce a non-aromatic productstream substantially free of solvent as an overhead stream, and a secondrich Water stream containing extracted solvent which is withdrawn fromthe second wash zone at the lower end thereof.

In the practice of the present invention the first and second rich waterstreams are handled in separate ways. The first rich water stream iswithdrawn from the first wash zone and is passed into a Water strippercolumn which is operated as a steam stripper under conditions sufficientto strip out and remove residual hydrocarbons from the first rich Waterstream. The overhead from the water stripper column, containing aconcentrate of the hydrocarbons, is withdrawn as a vapor stream andadmixed with the previously mentioned vapor stream from the extractivastripper column and commonly condensed as hereinabove described. Thebottom portion of the water stripper comprises Water containingsulfolane and is conventionally introduced into a steam generatorwherein it is converted into steam for use in the aromatic and solventrecovery column previously mentioned, Therefore, in a preferredembodiment of this invention, the bottoms from the water stripper columnare introduced as steam into the aromatic recovery column for Y use asstripping steam therein.

The second rich water stream which is withdrawn from the second waterwash column is passed into a separate fractionation column which ismaintained under distillation conditions including reboiling of thebottoms and reflux introduction into the top of the column. Operatingconditions are maintained in this second rich water fractionationcolumn, such as 230 F. and 20 p.s.i.a. in the bottom thereof, sufiicientto produce a distillate fraction comprising water substantially free ofsolvent. The distillate fraction is then passed into the upper portionof the second wash column as the second wash water in the mannerdiscussed hereinabove. The bottom from the fractionation column,containing water contaminated with significant quantities of sulfolane,is introduced into a steam generator for the generation of steam thereinin a manner so that the generated steam is also introduced into thesolvent and aromatic recovery column together with the steam generatedfrom the bottoms of the water stripper column previously mentioned.

Returning now to the aromatic and solvent recovery column: the overheadfrom the recovery column comprises substantially pure aromatichydrocarbons and steam as a vapor fraction. The vapor fraction iscondensed into an aromatic hydrocarbon product stream which is separatedfrom the condensed steam or condensate. The aromatic hydrocarbons arewithdrawn and recovered as a separate product stream. The condensate iswithdrawn and introduced into the first wash column as the specifiedfirst wash water for contacting of the raffinate phase in the mannerdiscussed hereinabove. If desired, a portion of the condensate may bepassed directly into the second rich Water fractionation column asadditional feed thereto. This latter alternative may be utilized if asignicant quantity of :wash water is needed in the second water washcolumn.

In summary, therefore, the present invention provides a method for theextraction and recovery of aromatic hydrocarbons which encompasses anovel water handling scheme operating in conjunction with a novelrafiinate water wash technique so that not only may high qualityaromatic hydrocarbons be produced, but also a nonaromatic hydrocarbonproduct stream which is substantially free of solvent contaminant. It isto be noted that the Water circuit is arranged so that contaminatingquantities of non-aromatic hydrocarbons are not introduced into thearomatic recovery column which, if permitted to happen, wouldcontaminate and lower the purity of the recovered aromatic hydrocarbons.It is also to lbe noted that the water circuit of the present inventionpermits maximum recovery of the solvent so that significant economy ofoperation in terms of minimum solvent loss may be realized.

The invention may be further understood with reference to the appendeddrawing which is a schematic representation of apparatus for practicingone embodiment of the invention.

DESCRIPTION OF THE DRAWING Referring now to the drawing, a hydrocarbonfeedstock containing aromatic hydrocarbons and non-aromatichydrocarbons, such as the desired product from a conventional catalyticreforming unit, comprising benzene, toluene, and xylene mixed withcorresponding naphthenes and paraflins enters the system via line 10 andintroduced into solvent extraction zone 11. Aqueous sulfolane as thelean solvent enters extractor 11 at an upper portion thereof via line 12and a relatively light nonaromatic hydrocarbon reflux, from a sourcehereinafter described, enters extractor 11 at the lower end thereof vialine 13. The raffinate stream comprising a concentrate of nonaromatichydrocarbons contaminated with, say, from 1% to 5% by volume sulfolaneis withdrawn from extractor 11 via line 28 for further processing inaccordance with the practice of this invention more fully developedhereinbelow.

An extract phase comprising sulfolane solvent having aromatichydrocarbons dissolved therein and which is contaminated with smallamounts of non-aromatic hydrocarbons, such as thecorrespondingnaphthenes and paraflins, is withdrawn from extractor 11via line 14, admixed with additional lean solvent from line 15, and thetotal admixture passed into extractive stripper column 17 via line 16.Suicient separation of distillation conditions, as previously mentioned,are maintained in extractive stripper 17 to produce a bottoms fractioncomprising solvent having dissolved therein the desired aromatichydrocarbons, such as benzene, toluene, and xylene, said bottoms beingremoved from distillation column 17 via line 20.

Ihe distillation conditions in extractive stripper 17 are alsosufficient to produce a distillate or overhead fraction comprisingessentially all of the non-aromatic hydrocarbons, aromatic hydrocarbons,and solvent. This overhead vapor fraction is withdrawn from stripper 17via line 18, admixed with an overhead vapor fraction from awater-stripper, more fully developed hereinbelow, from line 19,condensed for the removal of water by means not shown, and thehydrocarbon phase passed via line 13 as reux in'extractor 11, aspreviously mentioned.

Referring now to the solvent and aromatic hydrocarbon Astream in line20: this material is passed into aromatic and s olvent recovery column21 which is maintained under conditions suiiicient to separate thearomatic hydrocarbons from the solvent phase. The aromatic hydrocarbonsare concentrated as a distillate fraction in admixture with steam andremoved from recovery column 21 via line 22. The operation of recoverycolumn 21 includes the use of steam stripping on the column in order toremove the iinal traces of aromatic hydrocarbons from the solvent.Therefore, the lower end of column 21 includes inlet loci for `theintroduction of steam from a source hereinafter disclosed and thebottoms product from column 21 contains the desired solvent plus waterin suicient amounts such that this `bottom material in line 12 compriseslean solvent suitable for reuse in the extraction zone. The lean solventis passed via line 12 together with makeup lean solvent from line 33, ifany, into the upper portion of extractor 11 in the manner previouslydiscussed. Also, as needed, a portion of the material in line 12 isdiverted via line and 16 into extractive distillation column 17 in themanner previously discussed.

'Ihe material in line 22 contains a concentrate of aromatic hydrocarbonsand steam. This vapor stream is admixed with makeup water, as needed, ifany, from line 23 -condensed by means not shown, and passed via line 24into accumulator 25. Accumulator 25 is maintained under conditionssuicient to separate the steam condensate from the aromatichydrocarbonsthereby producing an aromatic hydrocarbon product stream which iswithdrawn from the system via line 26 and a steam condensate fractionwhich is withdrawn from accumulator 25 via line 27 for use in theraflinate water wash technique more fully developed hereinbelow.

l Returning now to extractor 11: the ratiinate phase which is withdrawnfrom extractor 11 via line 28 contains primarily non-aromatichydrocarbons together with small amounts of solvent andaromatichydrocarbons. 'Ihis rafnate stream is introduced into first wash column29 which may contain any suitable liquid-liquid contacting means, suchas Berl Saddles of Raschig ,Rings or may comprise a tower containingsuitable tray devices, or containing .a rotating disc contactor. A firstwater wash stream comprising the steam condensate from the aromaticrecovery column is introduced into the upper portion of iirst washcolumn 29 via line 27. The first water wash streampasses in downwardfashion in intimate contact with the upliowing 'raflinate stream in sucha manner that at least a significant portion of the contaminatingsolvent is absorbed into the aqueous phase. The resulting washed rainatestream comprising non-aromatic hydrocarbons having reduced sulfolanecontent leaves wash column 29 via line 34 and is passed into separatewash column 35 which may be identical to the conguration of wash column29. A second Water wash stream substantially free of sulfolane solventand obtained from a source hereinafter specified is introduced into washcolumn 35 via line 40. Suitable contacting conditions are maintained inwash column 3S so that substantially all of the remaining sulfolanesolvent contaminant is extracted by the water Wash stream therebyproducing a washed rainate product stream substantially free of solventwhich is withdrawn from the system via line 36.

The bottom aqueous stream from wash column 35 contains water and thesolvent which has been extracted. This second rich water stream isremoved from wash column 35 via line 37 and as needed admixed with Waterfrom line 38 and passed into fractionation column 39 which is maintainedunder water distillation conditions. The operating conditions aresuicient to produce an overhead water fraction substantially free ofsulfolane which is removed from column 39 via line `40 and passed intowash column 35 in the manner previously discussed. The |bottoms incolumn 39 comprises water` which contains the extracted sulfolanesolvent. 'Ihis bottoms material is removed from column 39 via line 41and passed into a steam generator, not shown, for the production ofsteam which is introduced into recovery column 21 in the mannerpreviously discussed. It is to be noted that the material in line 41 isfree of non-aromatic hydrocarbons and, therefore, in steam producedtherefrom would not offer a contaminant to the aromatic hydrocarbonswhich are being distilledin column 21.`

Returning now to first wash column 29: the aqueous stream accumulated inthe lower portion of column 29 contains water which has extracted asignificant quantity of the sulfolane contaminant from the raffinatephase. It also may contain significant quantities of entrainednonaromatic hydrocarbons and in some cases a small amount of aromatichydrocarbons. Accordingly, the material in line 30 is passed into waterstripper column 31 which operates under hydrocarbon stripping conditionsincluding the introduction of steam in such a manner that the overheaddistillate fraction produced comprises water, non-aromatic hydrocarbons,aromatic hydrocarbons, if any, and a small amount of solvent. Thisoverhead distillate fraction is removed via line 19 Iand admixed withthe overhead from the extractive distillation column 17 from line 18 andthe hydrocarbon phase processed, in the manner previously described, asreflux into extractor 11 via line 13. The bottoms material from waterstripper 31 contains water and sulfolane solvent and is passed via line32 into a steam generator, not shown, for the produc- Ytion of steamtherefrom which steam is also introduced into aromatic and solventrecovery `column 21 for use therein as stripping steam in the `mannerpreviously discussed.

It was found by operating the present invention in the manner describedthat the raiiinate in line 36 will contain less than 5 parts per millionof sulfolane solvent, and typically will contain less than l part permillion, e.g. 0.5 part per million of sulfolane. It was also found in acommercial version of this invention that as much as 50 to pounds perday of sulfolane solvent could be saved over the processing schemespracticed by the prior art heretofore.

PREFERRED EMBODIMENT Therefore, from the description presented thus far,a preferred embodiment of thisinvention provides a process for theextraction and recovery of monocyclic aromatic hydrocarbons from a feedmixture containing aromatic and non-aromatic hydrocarbons whichcomprises the steps of (a) introducing said feed mixture into a solventextraction zone maintained under aromatic hydrocarbon eX- tractionconditions including the presence of a sulfolanetype solvent sufcient toproduce an extract phase cornprising said solvent having aromaticlhydrocarbons dissolved therein and contaminated with non-aromatichydrocarbons, and a raffinate phase comprising non-aromatic hydrocarbonscontaminated with small quantities of said solvent; (b) passing saidextract phase into an extractive distillation zone under conditionssufficient to produce a first overhead fraction comprising a concentrateof nonaromatic hydrocabons, and a first bottoms fraction cornprisingsolvent having aromatic hydrocarbons dissolved therein; (c) passing saidbottoms fraction into fractionation means maintained under distillationconditions including the presence of stripping steam from a sourcehereinafter specified sufficient to produce a second overhead fractioncomprising a vapor said monocyclic aromatic hydrocarbons and steam, anda second bottoms fraction comprising lean solvent suitable for reuse insaid extraction zone; (d) condensing said second overhead fractionthereby producing a product stream of monocyclic aromatic hydrocarbons,and an aqueous condensate stream; (e) introducing said raffinate phaseinto a first Water wash zone in contact with at least a portion of saidcondensate stream of Step (d) under conditions sufficient to absorb atleast a portion of the solvent contaminant into the condensate stream;(f) withdrawing from said first wash zone a non-aromatic hydrocarbonstream having reduced solvent contaminant content, and a first richwater stream containing solvent and small quantities of non-aromatichydrocarbons; (g) passing said non-aromatic hydrocarbon stream into asecond water wash zone in contact with a hereinafter specified washwater stream under conditions sufficient to absorb substantially all ofthe remainder of said solvent contaminant into the wash water stream;(h) removing from said second wash zone a non-aromatic hydrocarbonstream substantially free of said solvent contaminant, and a second richWater stream containing solvent; (i) introducing said first rich waterstream into a stripping zone under conditions sufficient to produce athird overhead fraction comprising non-aromatic hydrocarbons, and athird bottoms fraction comprising water substantially free ofhydrocarbon contaminant; (j) introducing said second rich water streaminto a fractionation zone maintained under distillation conditionssufficient to produce a fourth overhead stream comprising water havingreduced solvent content, and a fourth bottoms fraction comprising waterof increased solvent content; (k) passing said fourth overhead streaminto said second water wash zone as the specified wash water stream;(l)introducing said third and fourth bottoms fraction said recoverymeans of Step (b) as the source of said stripping steam; and, (m)recovering said product stream of Step (c).

It is distinctly preferred that the solvent utilized in the practice ofthis invention comprise sulfolane.

The invention claimed:

1. Process for the extraction and recovery of aromatic hydrocarbons froma feed mixture containing aromatic and non-aromatic hydrocarbons with asulfolane-type solvent which comprises the steps of:

(a) introducing said feed mixture into a solvent extraction zonemaintained under aromatic hydrocarbon extraction conditions includingthe presence of said sulfolane solvent sufficient to produce an extractphase comprising said solvent having aromatic hydrocarbons dissolvedtherein, and a raffinate phase comprising non-aromatic hydrocarbonscontaminated with small quantities of said solvent;

(b) passing said extract phase into fractionation recovery means underfractionation conditions including the presence of stripping steam froma source hereinafter specified sufficient to produce a distillate vaporfraction comprising aromatic hydrocarbons and steam, and a bottomsfraction comprising lean solvent suitable for reuse in said extractionzone;

(c) condensing said distillate vapor fraction and producing thereby aproduct stream comprising aromatic hydrocarbons, and an aqueous stream;

(d) introducing said raffinate phase into a first wash zone in contactwith said aqueous stream of Step (c) under conditions sufficient toabsorb at least a portion of said contaminant into the aqueous stream;

(e) withdrawing from said first wash zone a non-aromatic hydrocarbonstream having reduced contaminant content, and a first rich Water streamcontaining solvent;

(f) passing said non-aromatic hydrocarbon stream into a second wash zonein contact with a hereinafter specified wash water stream underconditions suficient to absorb substantially all of the remainder ofsaid solvent contaminant into the wash water stream;

(g) removing from said second wash zone a non-aromatic hydrocarbonstream substantially free of said solvent contaminant, and a second richwater stream containing solvent;

(h) introducing said second rich water stream into a fractionation zoneunder fractionation conditions sufficient to produce a distillate waterstream substantially free of said solvent, and a bottoms streamcomprising water containing said solvent;

(i) passing said distillate Water stream of Step (h) into said secondwash zone as the specified wash water; and,

(j) introducing at least a portion of said first rich water stream andsaid bottoms stream of Step (h) into said recovery means of Step (b) asthe specified source of stripping steam.

2. Process according to claim 1 wherein said sulfolanetype solvent hasthe structural formula wherein R is selected from the group consistingof hydrogen, alkyl radical having from 1 to 8 carbon atoms, aryl radicalhaving from 1 to 10 carbon atoms, alkoxy radical having from 1 to 8carbon atoms, and arylalkyl radical having from 1 to 12 carbon atoms.

3. Process according to claim 2 wherein said solvent comprisessulfolane.

4. Process for the extraction and recovery of monocyclic aromatichydrocarbons from a feed mixture containing aromatic and non-aromatichydrocarbons which comprises the steps of:

(a) introducing said feed mixture into a solvent extraction zonekmaintained under aromatic hydrocarbon extraction conditions includingthe presence of a sulfolane-type solvent sufficient to produce anextract phase comprising said solvent having aromatic hydrocarbonsdissolved therein and contaminated with non-aromatic hydrocarbons, and araf-linate phase comprising non-aromatic hydrocarbons contaminated withsmall quantities of said solvent;

(b) passing said extract phase into an extractive distillation zoneunder conditions sufficient to produce a first overhead fractioncomprising a concentrate of non-aromatic hydrocarbons, and a firstbottoms fraction comprising solvent having aromatic hydrocarbonsdissolved therein;

(c) passing said bottoms fraction into fractionation means maintainedunder distillation conditions including the presence of stripping steamfrom a source hereinafter specified sufficient to produce a secondoverhead fraction comprising a vapor containing said monocyclic aromatichydrocarbons and steam, and a second bottom fraction comprising leansolvent suitable for reuse in said extraction zone;

(d) condensing said second overhead fraction there- 11 by producing aproduct stream of monocyclic aromatic hydrocarbons, and an aqueouscondensate stream;

(e) introducing said rainate phase into a rst water wash zone in contactwith at least a portion of said condensate stream of Step (d) underconditions sucient to absorb at least a portion of the solventcontaminant into the condensate stream;

(f) withdrawing from said rst wash zone a non-aromatic hydrocarbonstream having reduced solvent contaminant coutent, and a rst rich waterstream containing solvent and small quantities of non-aromatichydrocarbons;

(g) passing said non-aromatic hydrocarbon stream into a second Waterwash zone in contact with a hereinafter specified wash water streamunder conditions suiicient to absorb substantially all of the remainderof said solvent contaminant into the wash water stream;

(h) removing from said second wash zone a non-aromatic hydrocarbonstream substantially free of said solvent contaminant, and a second richwater stream containing solvent;

(i) introducing said first rich water, stream into a stripping zoneunder conditions suflicient to produce a third overhead fractioncomprising non-aromatic hydrocarbons, and a third bottoms fractioncomprising water substantially free of hydrocarbon contaminant;

(j) introducing said second rich water stream into a fractionation zonemaintained under distillation conditions suicient to produce a fourthoverhead stream comprising water having reduced solvent content, and afourth bottoms fraction comprising water of i11- creased solventcontent;

(k) passing said fourth overhead stream into said sec ond water washzone as the specified wash water Stream;

(l) introducing said third and fourth bottoms fraction into saidrecovery means of Step (c) as the source of said stripping stream; and,

(m) recovering said product stream of Step (d).

5. Process according to claim 4 wherein said sulfolanetype solvent hasthe structural formula wherein R is selected from the group consistingof hydrogen, alkyl radical having from 1 to 8 carbon atoms, aryl radicalhaving from l to 10 carbon atoms, alkoxy radical having from 1 to 8carbon atoms, and arylalkyl radical having from 1 to 12 carbon atoms.

6. Process according to claim 5 wherein said solvent comprisessulfolane.

7. Process according to claim 4Wvherein said irst overhead fraction ofStep (b) and said third overhead fraction of Step (i) are passed intosaid extraction zone of Step (a) as reux therein.

References Cited UNITED STATES PATENTS 3,179,708 5/ 1965 Pensten 208-3213,209,047 9/ 1965 Young 208-321 3,338,823 8/1967 Voetter 208-3213,338,824 8/ 1967 Oliver 20S-321 3,361,664 11/1968 Broughton et al.208-321 v3,436,435 4/1969 Tassell 208-321 3,461,066 4/1969 Morris et al.208-321 3,476,681 11/ 1969 Davies etal. 208-321 HERBERT LEVINE, PrimaryExaminer U.S. Cl. X.R.

